1. Field of the Invention
The present invention relates to a pattern inspection apparatus and a pattern inspection method. For example, it relates to an inspection apparatus that inspects a pattern based on an optical image of a pattern image acquired by using an illumination light and to a method thereof.
2. Description of Related Art
In recent years, with high integration and large capacity of large scale integrated (LSI) circuits, the line width (critical dimension) required for circuits of a semiconductor element is becoming narrower and narrower. Such a semiconductor element is manufactured by exposing (transferring) a pattern onto a wafer to form a circuit by a reduced projection exposure apparatus, known as a stepper, by using an original or “master” pattern with a circuit pattern formed thereon. The original pattern is also called a mask or a reticle, and hereinafter generically referred to as a mask. Therefore, in manufacturing a mask for transferring such a fine circuit pattern onto a wafer, a pattern writing apparatus using electron beams capable of writing or “drawing” fine circuit patterns needs to be employed. Pattern circuits may be written directly onto a wafer by the pattern writing apparatus. In addition to the writing apparatus using electron beams, a laser beam writing apparatus which uses laser beams for writing patterns is also under development.
Since the LSI manufacturing requires a tremendous amount of manufacturing cost, it is crucial to improve its yield. However, as represented by a 1 gigabit DRAM (Dynamic Random Access Memory), the order of a pattern constituting an LSI has been changing from submicron to nanometer dimensions. One of major factors that decrease the yield of the LSI manufacturing is a pattern defect of a mask used when exposing (transferring) a fine pattern onto a semiconductor wafer by the photolithography technology. In recent years, with miniaturization of an LSI pattern formed on a semiconductor wafer, dimensions to be detected as a pattern defect have become extremely small. Thus, a pattern inspection apparatus for inspecting defects of a mask for exposure used in manufacturing LSI needs to be highly accurate.
Meanwhile, with development of multimedia technology, the size of LCD (Liquid Crystal Display) substrates is becoming larger, e.g., 500 mm×600 mm or greater, and the size of a pattern such as a TFT (Thin Film Transistor) or the like formed on the liquid crystal substrate is becoming finer. Therefore, it is increasingly required that an extremely small defect of a pattern should be inspected in a large range. For this reason, development of a pattern inspection apparatus that efficiently and short-timely inspects a defect of a pattern of a large area LCD and a defect of a photo mask used in manufacturing the large area LCD is urgently required.
As inspection methods, it is known that an optical image of a pattern formed on a target object or “sample”, such as a lithography mask, imaged at a predetermined magnification using a magnifying optical system is compared with design data, or that optical images of identical patterns on the target object are compared. For example, the following is known as pattern inspection methods: die-to-die inspection method that compares data of optical images of identical patterns at different positions on the same mask, and die-to-database inspection method that inputs, into the inspection apparatus, writing data (design pattern data) which is generated by converting pattern-designed CAD data to an appropriate format to be input into the writing apparatus when writing a pattern on a mask, generates design image data (reference image) based on the input writing data, and compares the generated design image data with an optical image (serving as measured data) obtained by imaging the pattern. According to the inspection method of the inspection apparatus, a target object is placed on the stage so that a light flux may scan the object by the movement of the stage in order to perform an inspection. Specifically, the target object is irradiated with a light flux from the light source and the illumination optical system. Light transmitted through the target object or reflected therefrom is focused on a sensor through the optical system. An image captured by the sensor is transmitted as measured data to the comparison circuit. In the comparison circuit, after position alignment of the images, measured data and reference data are compared in accordance with an appropriate algorithm. If there is no matching between the data, it is judged that a pattern defect exists.
Laser light is used for performing the pattern inspection described above. Laser light generated and emitted from the light source is divided by using an integrator lens, and then, the divided lights illuminate, in an overlapping manner, the surface of the target object by an optical system such as a condenser lens. However, in such a configuration, illumination intensities at a plurality of focal points formed by the integrator lens are high, which causes a problem of degrading optical elements arranged near the focal points.
Although not related to a pattern inspection apparatus, there is disclosed a device for detecting the height of a target object, where an illumination optical system that divides a laser light by using an integrator lens is mounted (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2011-053120).